Bats are some of the most distinctive mammals around. The only ones capable of powered flight, bat species occupy a variety of ecological niches, from predator to pollinator. The different habits come with some significant specializations, like echolocation and the ability to hibernate through cold weather.

Part of the reason that bats have evolved such extensive specializations is that they've been around for a while—fossil evidence dates back over 50 million years. But now, thanks to our ability to sequence genomes, some researchers have provided a new picture of how bats manage to adapt to such distinctive lifestyles. The DNA sequences suggest that all bats share some adaptations that help them cope with the metabolic demands of flight, while individual species have other adaptations that help them handle echolocation and hibernation.

The work was done by a large international consortium that involved everyone from the BGI (formerly Beijing Genomics Institute) to the Naval Medical Research Center. The team picked two different species of bat: an insectivorous hibernator called Myotis davidii and the black flying fox, Pteropus alecto. The latter feeds on fruit and nectar, and lacks the former's ability to echolocate.

The sequence confirmed that the bats (technically Chiroptera) belong to a large group of mammals called the Pegasoferae that includes the carnivores as well as hoofed mammals like cows and horses. Molecular clock data suggest that bats shared their last common ancestor with horses about 85 million years ago, when the dinosaurs were still around. The split with carnivores was only slightly more recent.

Compared to other mammals, the bat genome is a bit small at 2 billion base pairs (humans, in contrast, have a bit over 3 billion). This may be a product of the high metabolic demands of flight, which make the energy involved in copying unnecessary DNA unfavorable. That doesn't mean that the genome is completely streamlined, though; the flying fox's genome ended up with over 125 copies of a relative of herpesvirus 2 at some point in its past.

A compact genome isn't the only thing that helps bats cope with the energy involved in flight. High metabolic exertion tends to produce oxygen radicals, which damage cellular components, including DNA. So, the authors tested whether the genes that are involved in maintaining DNA integrity showed signs of having undergone evolutionary selection (we've explained how to do that test in the past). Many of the genes involved in repairing DNA damage did show signs of selection, as did genes that help stop cells from dividing if they've picked up too much damage. Both species have also lost a gene that helps cells trigger an inflammatory response when they sense DNA outside of the cell's nucleus.

There were some hints of the two species' specialization in the genome as well. The insect eater has to digest a variety of cellular components, and ended up with four copies of an enzyme that breaks down nucleic acids. In contrast, the flying fox, which gets its energy from sugars in fruit and nectar, had a mutation completely inactivate the gene. The insect eater is also a hibernator, and had acquired extra copies of a gene that's involved in digesting fats. (Gene duplications seem to provide a simple way of ensuring cells produce more of an important protein; they've been found to help bacteria adapt to metabolic demands, too.)

There's also a hint of a change that may contribute to echolocation in the insect-eater. FOXP2 has been implicated in language use in humans and seems to have some distinctive changes in other species that use vocalizations for various purposes. The version of the gene carried by the echolocating species seems to have picked up an unusual number of changes compared to other mammalian species.

The work provides another indication of how flexible genomes can be. Although there are lots of notable differences, the genome as a whole clearly looks a lot like those of other mammals. Most of the obvious adaptations don't involve changing the basic gene content. Rather, they seem to alter the level and function of the proteins the genes code for; other changes have been identified in bats that affect the timing and location of gene expression as well. As we well know, evolution can accomplish a lot by tweaking a common genetic toolkit.

Something keeps blowing the laws of thermodynamics out of the water. How did we go from the Big Bang to all this ever-evolving and increasing higher order? Whatever it is, I love it and need some evolving myself.

Something keeps blowing the laws of thermodynamics out of the water. How did we go from the Big Bang to all this ever-evolving and increasing higher order? Whatever it is, I love it and need some evolving myself.

What exactly is blowing the laws of thermodynamics out of the water? Here's one of my favorite examples from undergrad physics--you can locally decrease the entropy of your apartment by cleaning it, but the entropy didn't just disappear. You had to burn calories, the dirt was transferred from your floor to a vacuum cleaner, etc.

(Another good example: parallel parking being hard is an example of entropy. There's a lot more ways to not be in the parking spot than there are to be in the parking spot.)

Something keeps blowing the laws of thermodynamics out of the water. How did we go from the Big Bang to all this ever-evolving and increasing higher order? Whatever it is, I love it and need some evolving myself.

What exactly is blowing the laws of thermodynamics out of the water?

Thanks Eurynom0s. Your examples are good.

I thought the second law of thermodynamics basically says that we're living in a universe that is becoming ever more disordered. Yet these bats seem to be an example of (self-organizing) order, and they are far from the only exception.

I thought the second law of thermodynamics basically says that we're living in a universe that is becoming ever more disordered. Yet these bats seem to be an example of (self-organizing) order, and they are far from the only exception.

But the universal entropy is still increasing because of the amounts of heat and energy transferred by cellular mechanisms in the bat's body to correct the errors in its DNA. Where does that heat and energy go? That was Eurynom0s' point. If you look hard enough, you'll find that the entropy is not decreasing after all, no matter how much it looks like order is being spontaneously generated from chaos.

I thought the second law of thermodynamics basically says that we're living in a universe that is becoming ever more disordered. Yet these bats seem to be an example of (self-organizing) order, and they are far from the only exception.

But the universal entropy is still increasing because of the amounts of heat and energy transferred by cellular mechanisms in the bat's body to correct the errors in its DNA. Where does that heat and energy go? That was Eurynom0s' point. If you look hard enough, you'll find that the entropy is not decreasing after all, no matter how much it looks like order is being spontaneously generated from chaos.

Exactly. The UNIVERSE is becoming ever more disordered. You're allowed to decrease entropy locally, but you're dumping it into the rest of the universe in the process.

Good article, but the evidence for selection does not indicate that bats ESPECIALLY evolved to handle DNA damage. We would need to know whether these genes are evolving faster than the same genes in comparable non-flying species, and normalize against the mutation rate in the rest of the genome. As it is written, there is evidence that DNA repair genes are under selective pressure, but that is almost obviously going to be true.I'm not even convinced that high-energy usage in muscle releases dangerous free radicals. There is strong selection to prevent that from happening.

1) If excessive exercise causes oxidation leading to DNA damage, is it better to be lazy and meditate in stillness, focusing on positive thoughts to maximize on endorphins instead of the worries that impart cortisol, in order to live longer?

2) Since diet helped to deactivate certain genes, did eating Kosher foods help evolve us to produce children with a higher IQ than the rest of the population? The RNA fragments we digest and deposit in our fat stores has some electrical imprinting on it due to intent.

Now, how do bats evolve into different strains, again? Necessity and taste?

To point #1, I'd have to say yes. Exercise is good, but excessive exercise is not so good. Excessive anything isn't good. Meditation is very helpful, and I think everyone should be doing it.

I like the idea of intent in point #2. I think that's actually what drives a lot of evolution. As for food, it's true that you are what you eat. Cells don't spring up out of nowhere. I'd like to see a longitudinal study done on vegetarians vs. carnivores to see if being a vegetarian imparts any positive benefit, either short- or long-term.

I realize this post and the one I'm responding to are edging toward metaphysics. That's fine with me.

Vapur9 wrote:

A couple issues:

1) If excessive exercise causes oxidation leading to DNA damage, is it better to be lazy and meditate in stillness, focusing on positive thoughts to maximize on endorphins instead of the worries that impart cortisol, in order to live longer?

2) Since diet helped to deactivate certain genes, did eating Kosher foods help evolve us to produce children with a higher IQ than the rest of the population? The RNA fragments we digest and deposit in our fat stores has some electrical imprinting on it due to intent.

Now, how do bats evolve into different strains, again? Necessity and taste?

To point #1, I'd have to say yes. Exercise is good, but excessive exercise is not so good. Excessive anything isn't good. Meditation is very helpful, and I think everyone should be doing think about it.

Something keeps blowing the laws of thermodynamics out of the water. How did we go from the Big Bang to all this ever-evolving and increasing higher order? Whatever it is, I love it and need some evolving myself.

Lots of good answers to your question above however, I will take it from a slightly different perspective. The Second Law of Thermodynamics only applies to closed systems. In an open system like the Earth, energy is input from the sun and output by heat radiated into space. The Second Law, short term from the perspective of those on the Earth, is more, the Second suggestion.

Nice article. I forwarded it to my girlfriend, who's currently researching genome size in birds, and she had the following minor correction -- the cost of *copying* the genome is relatively minor:

"Flight selects for high metabolic rate. Which requires greater efficiency. Which selects for smaller cells because greater surface area:volume ratio is more energetically efficient. Which selects for smaller nuclei and thus smaller genomes."

R.e. diet and ROS -- I found a few papers via Google scholar that establish connections here, e.g. for preeclampsia in humans: "The maternal diet is an underlying factor that provides an environment for free radical generation." (http://ajcn.nutrition.org/content/81/6/1390.short).

R.e. Exercise: There's been a lot of debate about this. In humans, the *benefits* of vigorous exercise generally outweigh the costs by a long-shot. Damage from ROS is slow and cumulative, whereas heart attacks, strokes, and diabetes can cause damage rapidly. Also, we have lots of pathways to deal with ROS under "normal" circumstances. The question is how far outside the envelope can you go. Hummingbird wing muscle, for example, hits extraordinary metabolic rates in-flight compared to us. Here's a quote from a nice review of exercise vs ROS for human skeletal muscle:"It is important to keep in mind that the extent of cell oxidative damage is determined by the rate of not only ROS production, but also ROS removal, provided by the antioxidant defense systems (including the capacity to repair the damage)."http://onlinelibrary.wiley.com/doi/10.1 ... 896.x/full

I wonder how bats became the only other animal besides birds and insects to evolve the ability to fly. Flying always seemed to me to be too much of a delicate evolutionary process with all the balancing needs like weight, balance, energy, etc that I'm surprised another animal just randomly evolved it too.

Something keeps blowing the laws of thermodynamics out of the water. How did we go from the Big Bang to all this ever-evolving and increasing higher order? Whatever it is, I love it and need some evolving myself.

What exactly is blowing the laws of thermodynamics out of the water? Here's one of my favorite examples from undergrad physics--you can locally decrease the entropy of your apartment by cleaning it, but the entropy didn't just disappear. You had to burn calories, the dirt was transferred from your floor to a vacuum cleaner, etc.

(Another good example: parallel parking being hard is an example of entropy. There's a lot more ways to not be in the parking spot than there are to be in the parking spot.)

That thermodynamics question always bugs me. The universe is a big place. It can easily hold areas of vastly increased useful heat. It's only the entire system that matters, not specific areas within the system.

Also, depending on your definition of "fly", you might reasonably include fish (http://en.wikipedia.org/wiki/Flying_fish). That means that few evolutionary lineages of animals *don't* have a species that exhibits some form of powered flight.

If you take "flight" to include passive aerial locomotion, then you get plants, fungi, spiders. Even mollusks can fly, as eggs attached to the legs of birds!

The evolutionary trail is pretty sparse, and understandably so. To really piece together the evolutionary story, you'd need to have the genomes of all the ancestors dating back 50 million years or so and then map out the specific changes that occurred in the genome. But, that would only tell a small portion of the story because science can't look at a genome and tell you how and when genes are expressed, and what they would actually do. For example, with respect to the bat. science doesn't know what echo location looks like at the genomic level, nor can it point to the region of the genome that builds machines that can repair damaged DNA.

Its a bit like looking at the byte codes of a compiled program, and trying to figure out what the program does without knowing the underlying machine that interprets the byte codes or the common libraries and hardware that the program runs on. Speculating that the genome of the bat is smaller due to selective pressure due to the energy demands of copying is counter-productive and ascribes to evolution more than is actually known.

Its a bit like looking at the byte codes of a compiled program, and trying to figure out what the program does without knowing the underlying machine that interprets the byte codes or the common libraries and hardware that the program runs on. Speculating that the genome of the bat is smaller due to selective pressure due to the energy demands of copying is counter-productive and ascribes to evolution more than is actually known.

Nice metaphor there. I agree with you up to the last sentence. Yes, copying is *not* the dominant cost (as I noted in several posts ago). The evolutionary pressures on genome size, however, are well established. Take a look here: http://www.gregorylab.org/research/

You're welcome to provide evidence to the contrary, as well as share your qualifications for making such broad claims

I wonder how bats became the only other animal besides birds and insects to evolve the ability to fly. Flying always seemed to me to be too much of a delicate evolutionary process with all the balancing needs like weight, balance, energy, etc that I'm surprised another animal just randomly evolved it too.

Sorry to break this to you, but insects are animals, too, and they evolved flight LONG before any vertebrates.

Also, as mentioned above, there were dinosaurs able to fly. And while true powered flight might be rather rare at the moment in vertebrates, there are several vertebrate gliders, and it's not hard to imagine some of them, given time and the right selection pressures, evolving powered flight.

Nice article. I forwarded it to my girlfriend, who's currently researching genome size in birds, and she had the following minor correction -- the cost of *copying* the genome is relatively minor:

"Flight selects for high metabolic rate. Which requires greater efficiency. Which selects for smaller cells because greater surface area:volume ratio is more energetically efficient. Which selects for smaller nuclei and thus smaller genomes."

I wonder how bats became the only other animal besides birds and insects to evolve the ability to fly. Flying always seemed to me to be too much of a delicate evolutionary process with all the balancing needs like weight, balance, energy, etc that I'm surprised another animal just randomly evolved it too.

Sorry to break this to you, but insects are animals, too, and they evolved flight LONG before any vertebrates.

Something keeps blowing the laws of thermodynamics out of the water. How did we go from the Big Bang to all this ever-evolving and increasing higher order? Whatever it is, I love it and need some evolving myself.

What exactly is blowing the laws of thermodynamics out of the water?

Thanks Eurynom0s. Your examples are good.

I thought the second law of thermodynamics basically says that we're living in a universe that is becoming ever more disordered. Yet these bats seem to be an example of (self-organizing) order, and they are far from the only exception.

Hasn't years of lab work shown the tendency of systems to move from 'disorder' to order?

I wonder how bats became the only other animal besides birds and insects to evolve the ability to fly. Flying always seemed to me to be too much of a delicate evolutionary process with all the balancing needs like weight, balance, energy, etc that I'm surprised another animal just randomly evolved it too.

Sorry to break this to you, but insects are animals, too, and they evolved flight LONG before any vertebrates.

Insects are VERY different from mammals so you really can't compare them cuz you'd be comparing apples to oranges.

I thought the second law of thermodynamics basically says that we're living in a universe that is becoming ever more disordered. Yet these bats seem to be an example of (self-organizing) order, and they are far from the only exception.

Also, depending on your definition of "fly", you might reasonably include fish (http://en.wikipedia.org/wiki/Flying_fish). That means that few evolutionary lineages of animals *don't* have a species that exhibits some form of powered flight.

If you take "flight" to include passive aerial locomotion, then you get plants, fungi, spiders. Even mollusks can fly, as eggs attached to the legs of birds!

If the flying fish counts, then more mammals can fly. Flying squirrels fly just as well as flying fish do!

I only want one example; this is for my own personal curiosity. Sound horrendously complicated, but I'll muddle through.

It's quite not that simple. It's not the base pairs that directly generate the observable traits, but rather the proteins that they code for. We're at the level where we know what base pairs correlate with which amino acids comprising the protein, but it's difficult to model what the final form of that protein looks like (hence projects like Folding@Home), let alone predict what exactly the protein does.

That's why it's easier to do comparative genomic studies like this, where we can identify what genes might control without having to do a bottoms-up simulation of what the DNA codes for. A software analogy might be something like looking at a list of the functions represented in a program, rather than the binary (it's a rather poor analogy, since software analogies start to break down when you get to this level).

Nice article. I forwarded it to my girlfriend, who's currently researching genome size in birds, and she had the following minor correction -- the cost of *copying* the genome is relatively minor:

"Flight selects for high metabolic rate. Which requires greater efficiency. Which selects for smaller cells because greater surface area:volume ratio is more energetically efficient. Which selects for smaller nuclei and thus smaller genomes."

I agree the cost of selecting for genome size is relatively minor, which is why we've got all this junk. But my understanding was flying animals are one of those edge cases where it starts to become apparent.

I had heard the cell size argument before, but my understanding was that it didn't make sense, given that muscles would be most sensitive to this, and they're huge, and formed through the fusion of multiple cells. As such, the size of the nucleus doesn't contribute to efficiency.

Something keeps blowing the laws of thermodynamics out of the water. How did we go from the Big Bang to all this ever-evolving and increasing higher order? Whatever it is, I love it and need some evolving myself.

Gah, I'm so tired of hearing this misunderstanding of the relationship between life and entropy. One more time:

First of all, you have a misconception of the entropy of the Big Bang. The Big Bang is the point of *highest* order that the universe has ever had- everything was at the same point at the same time, which is perfectly ordered, lowest entropy. Everything since has increased that entropy.

Secondly, there isn't "all this ever-evolving and increasing higher order". The amount of order relative to disorder in the universe is tiny, and ever decreasing. How much life is there versus dead matter? Almost none. You are just looking only at the low entropy life and ignoring all the endlessly vast amounts of disorder all around it.

Life works by specifically taking advantage of the laws of thermodynamics in the following very simple way: to make something with more order/less entropy, you just have to create even *more* disorder/high entropy, like a pump, so there is still a net increase in entropy, and a net increase in disorder.

Simple example with bats: you look at bats and you see something with high order/low entropy, but you are ignoring the fact that to make those bats required converting a much larger amount of insects and fruit into *vast* piles of bat poop and decomposed ex-bats. The mass of bat poop in the world is much larger than the mass of the bats in the world, and the increase in disorder in that poop is much larger than the increase in order in the bats.

The main thing to remember about life is: living things make the universe's disorder increase *faster*. We create small areas of order by creating large amounts of disorder.